1. Field of the Invention
The present invention relates to biosensors based on integrated optical waveguides, and more particularly, to surface plasmon resonance interferometric detection sensors formed by an array of planar waveguides.
2. Description of Related Art
Surface plasmon resonance (SPR) devices have shown high sensitivity in the detection of chemical and biological agents. Conventional SPR devices are based on sensing the reflectance change of mono- or polychromatic light, which undergoes total internal reflection at the hypotenuse of a prism, which is coated with a thin metal film. At certain angles of incidence for a given wavelength of light, the incident light with polarization in the plane of incidence is in resonance with the surface plasmon of the metal film. The term “surface plasmon” describes the collective longitudinal oscillation of the electrons in the metal film. The angle of incidence for the wavelength of the light at which this surface plasmon resonance occurs is very sensitive to the dielectric constant of the immediate environment of the thin metal film, which can be changed by a change in the index refraction of the surrounding material or chemical bonding of material deposited onto the metal layer.
Free space SPR interferometry techniques, such as SPR ellipsometry, optical heterodyning, and mapping the spatial intensity distribution, are cumbersome to be incorporated into compact SPR devices and exhibit high sensitivity to changes in the environment, such as temperature fluctuations. By contrast, a planar optical waveguide based SPR sensor operates similarly as a free space prism SPR device, but it offers higher sensitivity and is capable of being fabricated into multiple sensors on a single chip and can be easily integrated with fiber optical components, such as light sources and detectors.
Background information on a waveguide based SPR sensors that monitors the ratio of the transverse magnetic (TM) polarization and transverse electric (TE) polarization intensities is described in U.S. Pat. No. 5,606,633, issued Feb. 25, 1997, to Groger et al. “Chemical detector employing surface plasmon resonance excited using an optical waveguide configuration as an asymmetric waveguide coupler,” including the following, “the ratio of the TM and TE polarization intensities is monitored by a polarization beam splitter. The relatively unchanged TE polarization intensity serves as an integral reference for the sensor.”
The article “Surface plasmon resonance biosensor based on integrated optical waveguide” by J. Dostalek et al. (Sensors and Actuators, vol. B76, 2001, pages 8–12) describes the use of a broadband light source combined with spectral interrogation of SPR and demonstrates a detection sensitivity of 10−6 to a change in the index of refraction. Another SPR technology is based on detecting the phase-change of the light in a SPR sensor, which has been shown to significantly increase the detection sensitivity (P. Nikitin et al, “Surface plasmon resonance interferometer for biological and chemical sensing” Sensors and Actuators B., 1999, vol. 54, pp. 43–50).
Accordingly, a need exists to provide a highly sensitive surface plasmon waveguide arrayed sensor that simultaneously detects intensity and phase by planar light wave geometries. The present invention is directed to such a need.